The present invention involves an ultrasound Doppler method that permits noninvasive diagnosis and non-invasive unattended, continuous monitoring of vascular blood flow for medical applications.
Blood velocity monitoring is not currently practical for intensive care unit (ICU) or surgical applications. For non-invasive brain blood velocity monitoring, for example, a transcranial Doppler (TCD) probe must be mounted in a ball joint that is attached to the head by a helmet. The probe must be carefully aimed and fastened in place by an experienced person who knows how to locate the middle cerebral artery. Slight movements cause the probe to lose the blood velocity signal. Moreover, conventional Doppler ultrasound probes used in these devices scan (either mechanically or by using an acoustic phased array) in only one angle (which we will call azimuth), and will map only a single slice of the object being imaged.
Efforts have been made to modify such devices to provide real-time three dimensional (3-D) imaging. However, in order for a two dimensional (2-D) device to provide such imaging normally requires thousands of elements, and must form many thousands of pencil beams every ⅓0 second. Sensor cost grows with the number of elements in the array and the number of processing channels. Thus, such devices are cost prohibitive, as well as impractical.
Moreover, no automated procedure exists in current practice for precisely locating the optimum point at which to measure the Doppler signal. Conventional ultrasound Doppler-imaging devices can only measure radial velocity in blood vessels, and not the vector velocity or magnitude of the velocity of the blood.
Accordingly, what is needed is a new and useful Doppler ultrasound device and method that can automatically locate the optimum point at which to measure the Doppler signal, and thus provide medical providers with parameters such as vector velocity, the volume of blood passing through the blood vessel and the Doppler spectral distribution of the blood flow.
What is also needed is a new and useful Doppler ultrasound device and method that does not require it be placed on a patient with precision, and will enable a patient wearing the device to move freely.
The citation of any reference herein should not be construed as an admission that such reference is available as xe2x80x9cPrior Artxe2x80x9d to the instant application.
There is provided, in accordance with the present invention, a new, useful, and unobvious method of determining parameters of blood flow, such as vector velocity, blood flow volume, and Doppler spectral distribution, using sonic energy (ultrasound) and a novel thinned array. Also provided is a novel method of tracking blood flow and generating a three dimensional image of a blood vessel of interest that has much greater resolution than images produced using heretofore known ultrasound devices and methods.
Broadly, the present invention extends to a method for determining a parameter of blood flow in a blood vessel of interest, comprising the steps of:
a) providing an array of sonic transducer elements, wherein the element spacing in the array is greater than, equal or less than a half wavelength of the sonic energy produced by the elements, wherein at least one element transmits sonic energy, and a portion of the elements receive sonic energy;
b) directing sonic energy produced by the at least one element of the array into a volume of the subject""s body having the blood vessel of interest,
c) receiving echoes of the sonic energy from the volume of the subject""s body having the blood vessel of interest;
d) reporting the echoes to a processor programmed to
i) Doppler process the echoes to determine radial velocity of the blood flowing in the blood vessel of interest;
ii) calculate a three dimensional position of blood flow in the vessel of interest; and
iii) calculate the parameter of blood flow in the blood vessel at the three dimensional position calculated in step (ii); and
(e) displaying the parameter on a display monitor that is electrically connected to the processor.
Moreover, a method of the present invention permits an operator examining a subject to obtain information on blood flow in a particular region of the blood vessel of interest.
As used herein, the phrases xe2x80x9celement spacingxe2x80x9d and xe2x80x9cdistance between the elementsxe2x80x9d can be used interchangeably and refer to the distance between the center of elements of an array.
Various methods can be used to determine the three dimensional position of blood flow. In a particular embodiment, the method comprises the steps of having the processor programmed to:
i) determine a sum beam, an azimuth difference beam and an elevation difference beam from the echoes received from the blood vessel of interest;
ii) modulate the directions of the transmitted and received sonic energy based upon the sum, azimuth difference and elevation difference beams in order to lock on to the highest Doppler energy calculated from echoes from the flow of blood in the blood vessel of interest, and
iii) calculate the three dimensional position of the highest Doppler energy from the blood flow in the vessel of interest.
Optionally, the processor can also be programmed to determine at least one additional beam having an angle between the azimuth difference beam and the elevation difference beam prior to modulating the directions of the transmitted and received sonic energy, wherein the at least one additional beam is used to modulate the directions of the transmitted and received sonic energy. Naturally, the angle of the at least one additional beam can vary. In a particular embodiment, the at least one additional beam is at an angle that is orthogonal to the blood vessel of interest.
Moreover, the present invention extends to a method as described above, wherein steps (b) through (e) are periodically repeated so that the three dimensional position of blood flow in the vessel of interest is tracked, and the parameter of blood flow is periodically calculated and displayed on the display monitor. In a particular embodiment, the period of time between repeating steps (b) through (e) is sufficiently short so that the parameter being measured remains constant, e.g., 20 milliseconds.
The present invention further extends to a method for determining a parameter of blood flow in a particular region of a blood vessel of interest, comprising the steps of:
a) providing an array of sonic transducer elements, wherein the element spacing in the array is greater than, equal or less than a half wavelength of the sonic energy produced by the elements, wherein at least one element transmits sonic energy, and a portion of the elements receive sonic energy;
b) directing sonic energy produced by the at least one element of the array into a volume of the subject""s body having the particular region of the blood vessel of interest,
c) receiving echoes of the sonic energy from the volume of the subject""s body having the particular region of the blood vessel of interest;
d) reporting the echoes to a processor programmed to
i) Doppler process the echoes to determine radial velocity of the blood flowing in the particular region of the blood vessel of interest;
ii) calculate a three dimensional position of blood flow in the particular region of the blood vessel of interest; and
iii) calculate the parameter of blood flow in the particular region of the blood vessel of interest at the three dimensional position calculated in step (ii); and
(e) displaying the parameter on a display monitor that is electrically connected to the processor.
A particular method of calculating the three dimensional position of blow flow in such a method of the present invention comprises having the processor programmed to:
i) determine a sum beam, an azimuth difference beam and an elevation difference beam from the echoes received from the particular region of the blood vessel of interest;
ii) modulate the directions of the transmitted and received sonic energy based upon the sum, azimuth difference and elevation difference beams in order to lock on to the highest Doppler energy calculated from echoes received from the flow of blood in the particular region of the blood vessel of interest, and
iii) calculate the three dimensional position of the highest Doppler energy from the blood flow in the particular region of the blood vessel of interest.
As explained above, at least one additional beam can also be determined and used to calculate the three dimensional position.
Furthermore, the present invention extends to a method for determining a parameter of blood flow in a blood vessel of interest, comprising the steps of:
a) providing an array of sonic transducer elements, wherein the element spacing in the array is greater than, equal or less than a half wavelength of the sonic energy produced by the elements, wherein at least one element transmits sonic energy, and a portion of elements receive sonic energy;
b) directing sonic energy produced by the at least one element of the array into a volume of the subject""s body having the blood vessel of interest,
c) receiving echoes of the sonic energy from the volume of the subject""s body having the blood vessel of interest;
d) reporting the echoes to a processor electrically connected to the elements of the array, wherein the processor is programmed to
i) Doppler process the echoes to determine radial velocity of the blood flowing in the blood vessel of interest;
ii) determine a sum beam, an azimuth difference beam and an elevation difference beam from the echoes received from the blood vessel of interest;
iii) modulate the directions of the transmitted and received sonic energy based upon the sum, azimuth difference and elevation difference beams in order to lock on to the highest Doppler energy calculated from echoes from the flow of blood in the blood vessel of interest,
iv) calculate the three dimensional position of the highest Doppler energy from the blood flow in the vessel of interest; and
v) calculate the parameter of blood flow in the blood vessel at the three dimensional position calculated in step (iv); and
(e) displaying the parameter on a display monitor that is electrically connected to the processor.
As explained above, an operator performing a method of the present invention can obtain blood flow parameters from a blood vessel of interest, and even from a particular region of a blood vessel of interest.
Moreover, the present invention extends to a method for determining a parameter of blood flow in a particular region of a blood vessel of interest, comprising the steps of:
a) providing an array of sonic transducer elements, wherein the element spacing in the array is greater than, equal or less than a half wavelength of the sonic energy produced by the elements, wherein at least one element transmits sonic energy, and a portion of the elements receive sonic energy;
b) directing sonic energy produced by the at least one element of the array into a volume of the subject""s body having the particular region of the blood vessel of interest,
c) receiving echoes of the sonic energy from the volume of the subject""s body having the particular region of blood vessel of interest;
d) reporting the echoes to a processor electrically connected to the elements of the array, wherein the processor is programmed to
i) Doppler process the echoes to determine radial velocity of the blood flowing in the particular region of the blood vessel of interest;
ii) determine a sum beam, an azimuth difference beam and an elevation difference beam from the echoes received from the particular region of the blood vessel of interest;
iii) modulate the directions of the transmitted and received sonic energy based upon the sum, azimuth difference and elevation difference beams in order to lock on to the highest Doppler energy calculated from echoes from the flow of blood in the particular region of the blood vessel of interest,
iv) calculate the three dimensional position of the highest Doppler energy from the blood flow in the particular region of the blood vessel of interest; and
v) calculate the parameter of blood flow in the particular region of the blood vessel at the three dimensional position calculated in step (iv); and
(e) displaying the parameter on a display monitor that is electrically connected to the processor.
In another embodiment, the present invention extends to a device for determining a parameter of blood flow in a blood vessel of interest, comprising:
a) an array of sonic transducer elements, wherein the element spacing in the array is greater than, equal or less than a half wavelength of the sonic energy produced by the elements, and at least one element transmits sonic energy, and a portion of the elements receive sonic energy;
b) a processor electrically connected to the array so that echoes received from a volume of the subject""s body having the blood vessel of interest due to directing sonic energy produced by the at least one element of the array into the subject""s body is reported to the processor, wherein the processor is programmed to:
i) Doppler process the echoes to determine radial velocity of the blood flowing in the blood vessel of interest;
ii) calculate a three dimensional position of blood flow in the blood vessel of interest; and
iii) calculate the parameter of blood flow in the blood vessel of interest at the three dimensional position calculated in step (ii); and
(c) a display monitor that is electrically connected to the processor which displays the parameter of blood flow calculated by the processor.
A parameter of blood that can be determined with a device of the present invention includes blood flow volume, vector velocity, Doppler spectral distribution, etc. The parameter being measured can be an instantaneous value, or an average value determined over a heart cycle.
Moreover, the present invention extends to a device as described above, wherein the processor is programmed to:
i) determine a sum beam, an azimuth difference beam and an elevation difference beam from the echoes received from the blood vessel of interest after Doppler processing the echoes;
ii) modulate the directions of the transmitted and received sonic energy based upon the sum, azimuth difference and elevation difference beams in order to lock on to the highest Doppler energy calculated from echoes from the flow of blood in the blood vessel of interest,
iii) calculate the three dimensional position of the highest Doppler energy from the blood flow in the vessel of interest; and
iv) calculate the parameter of blood flow in the blood vessel of interest at the three dimensional position calculated in (iii).
Optionally, a processor of a device of the present invention can be further programmed to determine at least one additional beam having an angle between the azimuth difference beam and the elevation difference beam prior to modulating the directions of the transmitted and received sonic energy, wherein the at least one additional beam is used to modulate the directions of the transmitted and received sonic energy. In a particular embodiment, the at least one additional beam is at an angle that is orthogonal to the blood vessel of interest.
Moreover, in a another embodiment of a device of the present invention, the distance between the elements of the array is greater than xc2xd the wavelength of the sonic energy generated by the at least one element.
Furthermore, the present invention extends to a device for determining a parameter of blood flow in a blood vessel of interest, comprising:
a) an array of sonic transducer elements, wherein the element spacing in the array is greater than, equal or less than a half wavelength of the sonic energy produced by the elements, and at least one element transmits sonic energy, and portion of the elements receive sonic energy;
b) a processor electrically connected to the array so that echoes received from a volume of the subject""s body having the blood vessel of interest due to directing sonic energy produced by the at least one element of the array into the subject""s body is reported to the processor, wherein the processor is programmed to:
i) Doppler process the echoes to determine radial velocity of the blood flowing in the blood vessel of interest;
ii) calculate a three dimensional position of blood flow in the blood vessel of interest; and
iii) calculate the parameter of blood flow in the blood vessel of interest at the three dimensional position calculated in step (ii)
(c) a display monitor that is electrically connected to the processor which displays the parameter of blood flow calculated by the processor.
Particular parameters of blood flow that can be determined with a device of the present invention include, but certainly are not limited to blood flow volume, vector velocity, and Doppler spectral distribution. The parameter being measured can be an instantaneous value, or an average value determined over a heart cycle.
In addition, a processor of a device of the present invention can be further programmed to determine at least one additional beam having an angle between the azimuth difference beam and the elevation difference beam prior to modulating the directions of the transmitted and received sonic energy, wherein the at least one additional beam is used to modulate the directions of the transmitted and received sonic energy. In a particular embodiment, the at least one additional beam is at an angle that is orthogonal to the blood vessel of interest.
Moreover, the present invention extends to a method for generating a three dimensional image using sonic energy of a blood vessel of interest in a subject, the method comprising the steps of:
a) providing an array of sonic transducer elements, wherein the element spacing in the array is greater than, equal or less than a half wavelength of the sonic energy produced by the elements, wherein at least one element transmits sonic energy, and a portion of the elements receive sonic energy;
b) directing sonic energy produced by the at least one element of the array into a volume of the subject""s body having the blood vessel of interest,
c) receiving echoes of the sonic energy from the volume of the subject""s body having the blood vessel of interest;
d) reporting the echoes to a processor programmed to
i) Doppler process the echoes to determine radial velocity of the blood flowing in the blood vessel of interest;
ii) calculate a three dimensional position of blood flow in the blood vessel of interest;
iii) repeat steps (i) through (ii) to generate a plurality of calculated three dimensional positions; and
vi) generate a three dimensional image of the blood vessel of interest from the plurality of calculated three dimensional positions; and
(e) displaying the three dimensional image on a display monitor that is electrically connected to the processor.
Furthermore, the present invention permits an operator utilizing a method of the present invention to generate a three dimensional image of not only a blood vessel in the body, but even a particular region of a blood vessel in the body.
Numerous means available for calculating the three dimensional position of a blood vessel and even a particular portion of a blood vessel are encompassed by the present invention. A particular means comprises having the programmed processor:
i) determine a sum beam, an azimuth difference beam and an elevation difference beam from the echoes received from the blood vessel of interest after Doppler processing the echoes;
ii) modulate the directions of the transmitted and received sonic energy based upon the sum, azimuth difference and elevation difference beams in order to lock on to the highest Doppler energy calculated from echoes from the flow of blood in the blood vessel of interest, and
iii) calculate the three dimensional position of the highest Doppler energy from the blood flow in the vessel of interest, and
iv) repeat steps (i) through (iii) to generate a plurality of calculated three dimensional positions.
Optionally, a processor of a method of the present invention can also be programmed to determine at least one additional beam having an angle between the azimuth difference beam and the elevation difference beam prior to modulating the directions of the transmitted and received sonic energy, and the at least one additional beam is also used to modulate the directions of the transmitted and received sonic energy, and calculate the three dimensional position of the highest Doppler energy. In a particular embodiment, the at least one additional beam is at an angle that is orthogonal to the blood vessel of interest.
The present invention also extends to a method for generating a three dimensional image of a blood vessel of interest in a subject using sonic energy, the method comprising the steps of:
a) providing an array of sonic transducer elements, wherein the element spacing in the array is greater than, equal or less than a half wavelength of the sonic energy produced by the elements, wherein at least one element transmits sonic energy, and a portion of the elements receive sonic energy;
b) directing sonic energy produced by the at least one element of the array into a volume of the subject""s body having the blood vessel of interest,
c) receiving echoes of the sonic energy from the volume of the subject""s body having the blood vessel of interest;
d) reporting the echoes to a processor programmed to
i) Doppler process the echoes to determine radial velocity of the blood flowing in the blood vessel of interest;
ii) determine a sum beam, an azimuth difference beam and an elevation difference beam from the echoes received from a portion of the blood vessel of interest;
iii) modulate the directions of the transmitted and received sonic energy based upon the sum, azimuth difference and elevation difference beams in order to lock on to the highest Doppler energy calculated from echoes from the flow of blood in the blood vessel of interest,
iv) calculate the three dimensional position of the highest Doppler energy from the blood flow in the vessel of interest; and
v) repeat steps (i) through (iv) to generate a plurality of calculated three dimensional positions;
vi) generate a three dimensional image of the blood vessel of interest from the plurality of calculated three dimensional positions; and
(e) displaying the three dimensional image on a display monitor that is electrically connected to the processor.
Optionally, the three dimensional image can be of a particular region of a blood vessel of interest. Moreover, a processor of a method described herein can also determine at least one additional beam having an angle between the azimuth difference beam and the elevation difference beam prior to modulating the directions of the transmitted and received sonic energy, and the at least one additional beam is also used to modulate the directions of the transmitted and received sonic energy, and calculate the three dimensional position of the highest Doppler energy. Angles for use with the at least one additional beam are described above.
Moreover, in another embodiment of the present invention, the distance between the elements of the array is greater than xc2xd the wavelength of the sonic energy generated by the at least one element.
Furthermore, the present invention extends to a device generating a three dimensional image of a blood vessel of interest in a subject using sonic energy, comprising:
a) an array of sonic transducer elements, wherein the element spacing in the array is greater than, equal or less than a half wavelength of the sonic energy produced by the elements, and at least one element transmits sonic energy, and a portion of the elements receive sonic energy;
b) a processor electrically connected to the array so that echoes received from a volume of the subject""s body having the blood vessel of interest due to directing sonic energy produced by the at least one element of the array into the subject""s body is reported to the processor, wherein the processor is programmed to:
i) Doppler process the echoes to determine radial velocity of the blood flowing in the blood vessel of interest;
ii) calculate a three dimensional position of blood flow in the blood vessel of interest;
iii) repeat steps (i) through (ii) to generate a plurality of calculated three dimensional positions;
v) generate a three dimensional image from the plurality of calculated three dimensional positions, and
(c) a display monitor that is electrically connected to the processor which displays the three dimensional image.
As explained above, a device of the present invention permits an operator to generate and display three dimensional images of a blood vessel of interest, and even of a particular region of a blood vessel that the operator wants to investigate closely. Moreover, in a particular embodiment, a processor of a device of the present invention can be programmed to calculate the three dimensional position of a blood vessel by
i) determining a sum beam, an azimuth difference beam and an elevation difference beam from the echoes received from the blood vessel of interest after Doppler processing the echoes;
ii) modulating the directions of the transmitted and received sonic energy based upon the sum, azimuth difference and elevation difference beams in order to lock on to the highest Doppler energy calculated from echoes from the flow of blood in the blood vessel of interest,
iii) calculating the three dimensional position of the highest Doppler energy from the blood flow in the vessel of interest; and
iv) repeat steps (I) through (iii) in order to generate a plurality of calculated three dimensional positions used to generate the three dimensional image.
Optionally, the processor can be programmed to further determine at least one additional beam having an angle between the azimuth difference beam and the elevation difference beam prior to modulating the directions of the transmitted and received sonic energy, wherein the at least one additional beam is used to modulate the directions of the transmitted and received sonic energy. The angle between the azimuth difference beam and the elevation difference beam of the additional beam can vary. In a particular embodiment, the at least one additional beam is at an angle that is orthogonal to the blood vessel of interest.
Furthermore, the present invention extends to a thinned array for use in an ultrasound device, comprising a plurality of sonic transducer elements, wherein the element spacing in the array is greater than a half wavelength of the sonic energy produced by the elements, and the elements are positioned and sized within the array, and sonic energy is electronically steered by the elements so that any grating lobes produced by the sonic energy are suppressed. In a particular embodiment, the elements positioned and sized so that they are flush against each other.
Hence, the current invention performs blood velocity monitoring by collecting Doppler data in three dimensions; azimuth, elevation, and range (depth); so that the point (in three dimensional space) at which the velocity is to be monitored can be acquired and tracked when the patient or the sensor moves. The invention also produces a three dimensional map of the blood flow and converts measured radial velocity to true vector velocity.
Moreover, in this invention, once the desired signal is found, it will be precisely located and continually tracked with accuracy far better than the resolution. A heretofore unknown method to achieve sub-resolution tracking and mapping involves a novel and unobvious extension of a procedure called xe2x80x9cmonopulsexe2x80x9d. Monopulse tracking has been used in military applications for precisely locating and tracking a point target with electromagnetic radiation. However, it has never been utilized in connection with sonic waves to determine the velocity of moving fluids in vivo.
This invention provides: (1) affordable three-dimensional imaging of blood flow using a low-profile easily-attached transducer pad, (2) real-time vector velocity, and (3) long-term unattended Doppler-ultrasound monitoring in spite of motion of the patient or pad. None of these three features are possible with current ultrasound equipment or technology.
The pad and associated processor collects and Doppler processes ultrasound blood velocity data in a three-dimensional region through the use of a two-dimensional phased array of piezoelectric elements on a planar, cylindrical, or spherical surface. Through use of unique beamforming and tracking techniques, the invention locks onto and tracks the points in three-dimensional space that produce the locally maximum blood velocity signals. The integrated coordinates of points acquired by the accurate tracking process is used to form a three-dimensional map of blood vessels and provide a display that can be used to select multiple points of interest for expanded data collection and for long term continuous and unattended blood flow monitoring. The three dimensional map allows for the calculation of vector velocity from measured radial Doppler.
In a particular embodiment, a thinned array (greater than half-wavelength element spacing of the transducer array) is used to make a device of the present invention inexpensive and allow the pad to have a low profile (fewer connecting cables for a given spatial resolution). The array is thinned without reducing the receiver area by limiting the angular field of view. The special 2-D phased array used in this invention makes blood velocity monitoring inexpensive and practical by (1) forming the beams needed for tracking and for re-acquiring the blood velocity signal and by (2) allowing for an element placement that is significantly coarser than normal half-wavelength element spacing. The limited range of angles that the array must search allows for much less than the normal half wavelength spacing without reducing the total receiver area.
Grating lobes due to array thinning can be reduced by using wide bandwidth and time delay steering. The array, or at least one element of the array, is used to sequentially insonate the beam positions. Once the region of interest has been imaged and coarsely mapped, the array is focused at a particular location on a particular blood vessel for measurement and tracking. Selection of the point or points to be measured and tracked can be based on information obtained via mapping and may be user guided or fully automatic. Selection can be based, for example, on peak response within a range of Doppler frequencies at or near an approximate location.
In the tracking mode a few receiver beams are formed at a time: sum, azimuth difference, elevation difference, and perhaps, additional difference beams, at angles other than azimuth (=0 degrees) and elevation (=90 degrees). Monopulse is applied at angles other than 0 and 90 degrees (for example 0, 45, 90, and 135 degrees) in order to locate a vessel in a direction perpendicular to the vessel. When the desired (i.e. peak) blood velocity signal is not in the output, this is instantly recognized (e.g., a monopulse ratio, formed after Doppler filtering, becomes non-zero) and the array is used to track (slow movement) or re-acquire (fast movement) the desired signal. Re-acquisition is achieved by returning to step one to form and Doppler-process a plurality of beams in order to select the beam (and the time delay or xe2x80x9crange gatexe2x80x9d) with the most high-Doppler (high blood velocity) energy. This is followed by post-Doppler monopulse tracking to lock a beam and range gate on to the exact location of the peak velocity signal. In applications such as transcranial Doppler, where angular resolution based on wavelength and aperture size is inadequate, fine mapping is achieved, for example, by post-Doppler monopulse tracking each range cell of each vessel, and recording the coordinates and monopulse-pair angle describing the location and orientation of the monopulse null. With a three-dimensional map available, true vector velocity can be computed. For accurate vector flow measurement, the monopulse difference is computed in a direction orthogonal to the vessel by digitally rotating until a line in the azimuth-elevation or C-scan display is parallel to the vessel being monitored. The aperture is more easily rotated in software (as opposed to physically rotating the transducer array) if the aperture is approximately circular (or eliptical) rather than square (or rectangular). Also, lower sidelobes result by removing elements from the four corners of a square or rectangular array in order to make the array an octagon.
In this invention, as long as (1) a blood vessel or (2) a flow region of a given velocity can be resolved by finding a 3-D resolution cell through which only a single vessel passes, that vessel or flow component can then be very accurately located within the cell. Monopulse is merely an example of one way to attain such sub-resolution accuracy (SRA). Other methods involve xe2x80x9csuper-resolutionxe2x80x9d or xe2x80x9cparametricxe2x80x9d techniques used in xe2x80x9cmodern spectral estimationxe2x80x9d, including the MUSIC algorithm and autoregressive modeling, for example. SRA allows an extremely accurate map of 3-D flow.
Furthermore, the present invention utilizes post-Doppler, sub-resolution tracking and mapping; it does Doppler processing first and uses only high Doppler-frequency data.
This results in extended targets since the active vessels approximate xe2x80x9clinesxe2x80x9d as opposed to xe2x80x9cpointsxe2x80x9d. In three-dimensional space, these vessels are resolved, one from another. At a particular range, the monopulse angle axis can be rotated (in the azimuth-elevation plane) so that the xe2x80x9clinexe2x80x9d becomes a xe2x80x9cpointxe2x80x9d in the monopulse angle direction. That point can then be located by using super-resolution techniques or by using a simple technique such as monopulse. By making many such measurements an accurate 3-D map of the blood vessels results.
Methods for extending the angular field of view of the thinned array (that is limited by grating lobes) include (1) using multiple panels of transducers with multiplexed processing channels, (2) convex V-shaped transducer panels, (3) cylindrical shaped transducer panel, (4) spherical shaped transducer panel, and (5) negative ultrasound lens. If needed, moving the probe and correlating the sub-images can create a map of an even larger region.
Active digital beamforming can also be utilized, but the implementation depends on a choice to be made between wideband and narrowband implementations. If emphasis is on high resolution mapping of the blood vessels, then a wide bandwidth (e.g., 50% of the nominal frequency) is used for fine range resolution. If emphasis is on Doppler spectral analysis, measurement, and monitoring, the map is only a tool. In this case, a narrowband, low cost, low range-resolution, high sensitivity implementation might be preferred. A wideband implementation would benefit in performance (higher resolution, wider field of view, and reduced grating lobes) using time-delay steering while a narrowband implementation would benefit in cost using phase-shift steering. The invention can thus be described in terms of two preferred implementations.
In a wideband implementation, time delay steering can be implemented digitally for both transmit and receive by over-sampling and digitally delaying in discrete sample intervals. In a narrowband implementation, (1) phase steering can be implemented digitally (digital beamforming) for both transmit and receive, and (2) bandpass sampling (sampling at a rate lower than the signal frequency) can be employed with digital down-conversion and filtering.
Accordingly, it is an object of the present invention to locate the point in three dimensional space having the greatest high-Doppler energy, and determining coordinates for that point. With that information, and the radial velocity of the blood flowing through the blood vessel at that point, a variety of blood flow parameters can be calculated at that point, including, but not limited to vector velocity of blood flow, volume of blood flow, or Doppler spectral distribution. The parameter being measured can be an instantaneous value, or an average value determined over a heart cycle.
It is also an object of the present invention to continuously track and map in vivo the point in three dimensional space having the greatest Doppler-energy, and using the coordinates to generate a three dimensional image of a blood vessel and blood flow therein that possess a much greater resolution than images generated using heretofore known Doppler ultrasound methods and devices.
It is yet another object of the present invention to provide a thinned array which does not utilize the number of element transducers as are required with heretofore known Doppler ultrasound devices. As a result, the decreased number of elements in the array decreases size of the array utilized and provides a patient being analyzed with mobility that would not be available if using conventional ultrasound devices to obtain blood flow parameters such as vector velocity, blood flow volume, and Doppler spectral distribution. The parameter being measured can be an instantaneous value, or an average value determined over a heart cycle.